Deserializing std::map

[RolandasV]

• What is the issue you have?
  When trying to deserialize a std::map which has a int/Enum as a key I'm getting compilation error.
  Error C2166 l-value specifies const object

When i try to deserialize a std::map with a key as a string for example, it compiles fine.

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?
  Serialize a std::map having int/enum as a key. Try to deserialize it.

json.at(_materialTypeByFaceSelectionJson).get<map<MaterialTypeEnum, FaceSelectionEnum>>();

• What is the expected behavior?
  It should compile.

• And what is the actual behavior instead?
  It doesn't.

• Which compiler and operating system are you using? Is it a supported compiler?
  I'm using windows 10 and Visual Studio 2017.

• Did you use a released version of the library or the version from the develop branch?
  I'm using released version.

[theodelrieu]

There is an open PR to provide this feature: #1089

Could you try this commit and tell me if it fixes your issue?

[giumas]

@nlohmann: since I need this feature, I am wondering if the develop branch is reliable to use it (unless 3.1.3 is coming).

[nlohmann]

I hope to release 3.1.3 before the end of July.

[giumas]

If one of the map pairs (e.g., std::pair<int64_t, double>) has std::nan, it becomes a null in the written json.
If I read it back as a map, I get: [json.exception.type_error.302] type must be number, but is null.
What is the suggested approach in such a case? Should I iterate through each pair?

[giumas]

@nlohmann do you prefer that I move the described issue in a stand-alone ticket?

[nlohmann]

Yes, please.